xc2xa7 2.1 Field of the Invention
The present invention relates to the field of helical arrays, such as helical polymers and, in particular, uses helical arrays for temperature measurement, or temperature controlled optical switching.
xc2xa7 2.2 Related Art
The present invention manipulates and exploits properties of helical arrays. Generally, a helical array is a molecular or supramolecular arrangement that is helical. The helical array can comprise molecules that vary greatly in molecular weight, as, for example, from a very high molecular weight DNA, to an oligomer having a molecular weight of as little as a few hundred daltons, perhaps less. Generally, such helical arrays are formed by the repetitive connection, either by forming covalent bonds or by other kinds of molecular attachments, such as hydrogen bonds, of identical groups, or a limited number of different kinds of groups.
Helical polymers have been used in various capacities, including information storage (See, e.g., U.S. Pat. Nos. 5,750,049 and 5,480,749; both incorporated herein by reference.). In the inventions described in the identified patents, a property of helical polymers was shown to allow the invention of an optical switch effectuated by irradiating, with circularly polarized light, a polymer synthesized from racemic monomer units.
Liquid crystals formed by anisotropically shaped molecules may have a nematic phase or other achiral phases between a solid phase and an isotropic liquid phase. In a cholestric phase of a liquid crystal, elongated molecules, approximately parallel within a layer over short distances, twist from layer to layer, thereby taking the shape of helices, which will prefer one handedness over the other.
Helical polymers have a property referred to as their xe2x80x9csensexe2x80x9d. More specifically, helical polymers can have a right-handed sense or a left-handed sense. The inventors believe that such properties of helical polymers neither have been manipulated, nor exploited for purposes of temperature measurement.
Given a predefined temperature, the present invention describes a way to synthetically manipulate a helical array, in a rational manner based on principles of statistical physics, such that a property (e.g., optical activity) of the helical array has a predetermined value (e.g., zero) at the predefined temperature. If a different predefined temperature is desired, the helical array is further synthetically manipulated. A temperature measurement can then be made by quantitatively measuring if there is a deviation in the relevant property at temperatures above or below the predefined temperature, a technology not currently available.
The present invention provides a method for measuring temperature using helical polymers having attached molecular units, such molecular units favoring opposing helical senses. The molecular units may be chiral groups favoring different helical senses. Such chiral groups are structurally different, non-racemic molecules. The helical sense of the helical array varies as a function of temperature. The present invention also provides compositions of matter that can be used in the context of the inventive method.
In one embodiment of the present invention, temperature is determined based on optical activity, which changes as a function of relative helical sense. For example, temperature may be measured using a chiral optical effect of cooperative helical arrays subjected to a competition for helical sense between structurally different chiral non-racemic molecules. Such molecules are selected for their preference for one helical sense. The optical activity, which is a function of the relative proportion of each helical sense, therefore also varies as a function of the composition of the competing units. The present invention can therefore manipulate the helical array to have a predetermined optical activity (e.g., no optical activity) at a variety of temperatures. More specifically, the helical array can be manipulated by controlling the composition of the competing units attached to the helical array. In the case where the helical array is a helical polymer, this manipulation should be performed such that the predefined temperature is within the stability limits of the polymeric molecules. For example, for a polyisocyanate helical polymer, the predefined temperature may be from any low temperature up to about somewhat above the boiling point of water. As the temperature deviates from the predefined temperature at which there is no optical activity, the optical activity will then increase in the positive or negative direction (e.g., twist the plane of polarized light in opposite directions).
The effect of temperature on helical sense can be seen not only by measuring chiral optical properties, but also by the effect of the helical sense on a liquid crystal. In the liquid crystal case, at the specified temperature for a predetermined optical activity value (e.g., no optical activity), a nematic phase will be detected. If the temperature deviates from this set value, cholesteric phases of opposite pitch sense will be obtained. Alternatively, if the liquid crystal phase is smectic C, it would be transformed to smectic C*. Other alternatives may be encountered in liquid crystals exhibiting the effect of the helical senses transforming from equal population to unequal populations of varying proportions. The liquid crystal transformations may be observed in the manner appropriate to liquid crystals, which may involve direct observations or the chiral optical properties well known to be associated with chiral liquid crystals.
Thermally controlled optical switches are also described.
These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.